1. Field of the Invention
The present invention relates to a thin film transistor, a method of manufacturing the same and a flat panel display device having the same, and more particularly, to a thin film transistor having an oxide semiconductor as an active layer, a method of manufacturing the same and a flat panel display device having the same.
2. Discussion of Related Art
In general, a thin film transistor (TFT) includes an active layer providing channel, source and drain regions, and a gate electrode formed on the channel region and electrically insulated from the active layer by a gate insulating layer.
The active layer of the TFT described above is generally formed of a semiconductor material such as amorphous silicon or poly-silicon. At this time, if the active layer is formed of amorphous silicon, mobility is low, so that it is difficult to realize a driving circuit operating at a high speed. If the active layer is formed of poly-silicon, mobility is high while a threshold voltage is not uniform. Therefore, a separate compensation circuit should be added.
A conventional method of manufacturing a TFT using low temperature poly-silicon (LTPS) involves a high-cost process such as laser heat treatment, and is not easy to control characteristics. Therefore, it is difficult to apply the conventional method to a large-sized substrate.
In order to solve such a problem, studies on an oxide semiconductor used as an active layer have recently been conducted.
A TFT using a zinc oxide (ZnO) or oxide semiconductor containing ZnO as a main component as an active layer has been disclosed in Japanese Patent Publication No. 2004-273614.
An oxide semiconductor containing ZnO as a main component is estimated to be an amorphous and stable material. If such an oxide semiconductor is used as an active layer, a TFT can be manufactured using a conventional LTPS process, which can be performed at a low temperature of 300° C. or less.
However, in order to apply the oxide semiconductor containing ZnO as a main component to a device, it is required to develop a process satisfying electrical characteristics and improve characteristics in general. In addition, it is difficult to form an ohmic contact between a source/drain region and a metal electrode.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.